Play the next music in a list

[Pymax]

Hi everyone, I'm looking for a way to play the next music from a list. I use pygame.mixer to play a music from lists_of_songs, I can't find a way to play the next music in the list. Do you know a method or something to do that?
Here is my code if you want to have a look:

#!/usr/bin/env python3

# RFID
import RPi.GPIO as GPIO
from mfrc522 import SimpleMFRC522

# Sound
import os
import pygame

import threading
import time

tags = {
    '1006795053427': 'wild', #blue tag
    '526264140976': 'sport', #blue tag
    '584185304561': 'wild', # given to Valerie / Antoine
    '584185305597': 'sport', # given to Valerie / Antoine
    '584195095434': 'politic', # given to Valerie / Antoine
    '584195357686': 'wild',
    '584195619826': 'sport',
    '584195881982': 'politic',
    }

class Media ():
    def __init__(self):
        self.themes = []
        self.playing = False
        self.ready_to_play = False
        self.DELAY_BEFORE_TO_PLAY = 0.5
        self.t = None
        self.SOUND_PATH = "/tmp/IRMA/"

        pygame.init()
        pygame.mixer.init()

        self.ready_to_play = True

    def play_theme(self, theme):

        print("play_theme - theme:", theme)

        theme_path = self.SOUND_PATH + theme + "/"

        lists_of_songs = os.listdir(theme_path)

        for song in lists_of_songs:
            if self.playing == False:
                break
            if song.endswith(".mp3"):
                file_path = theme_path + song
                pygame.mixer.music.load(str(file_path))
                pygame.mixer.music.play()
                pygame.mixer.music.set_volume(1.0)
                print("play_theme - Playing::::: " + song)
                while pygame.mixer.music.get_busy() == True:
                    if self.playing == False:
                        break
                    time.sleep(0.05)

        print("play_theme - stop")
        pygame.mixer.music.stop()

        return 0

    def is_playing(self):
        return self.playing

    def is_ready(self):
        return self.ready_to_play
    
    def add(self, theme):
        if len(theme) > 20:
            return 1

        # only one theme
        '''
        if self.themes.count(theme) == 1:
            return 2
        '''
        self.clear()

        self.themes.append(theme)

        self.display()

        return 0

    def clear(self):
        self.themes.clear()

    def play(self):
        print("play - start")
        self.ready_to_play = False
        self.playing = True
        # No merge, for the moment
        # Only one tag
        #theme = self.merge_themes()
        theme = self.themes[0]
        self.play_theme(theme)

        self.playing = False
        self.ready_to_play = True
        print("play - end")

    def stop(self):
        print("stop")
        self.playing = False
        if self.t is not None:
            self.t.cancel()
            self.t = None
        #pygame.mixer.music.stop()
        print("stop ended")

    def play_delayed(self):
        print("play_delayed - start")
        while self.is_ready() is False:
            time.sleep(0.01)

        if self.t is not None:
            self.t.cancel()
            self.t = None
        self.t = threading.Timer(self.DELAY_BEFORE_TO_PLAY, self.play)
        self.t.start()
        print("play_delayed - end")

    def display(self):
        print("display - List:")
        for theme in self.themes:
            print("-", theme)
'''
    def merge_themes(self):
        # TODO: 0111
        if self.themes.count('wild') == 1:
            if self.themes.count('sport') == 1:
                return 'politic'
            elif self.themes.count('politic') == 1:
                return 'sport'
            else:
                return 'wild'
        elif self.themes.count('sport') == 1:
            if self.themes.count('politic') == 1:
                return 'wild'
            else:
                return 'sport'
        elif self.themes.count('politic') == 1:
            return 'politic'
'''

def read_tags(tags):
    try:
        reader = SimpleMFRC522()
    except:
        print("read_tags - init error")
        return 1

    media = Media()

    old_id = ''
    count_none = 0
    read_interval = 0.5 # 500ms

    while True:
        time.sleep(read_interval)
        #print("read_tags - Waiting tag...")
        try:
            id, text = reader.read_no_block() #reader.read()
        except:
            print("read_tags - error")
            id = None
            text = ""

        if id is None:
            if count_none < 3:
                count_none += 1
            elif count_none == 3 and media.is_playing():
                count_none = 0
                old_id = ''
                print("read_tags - media is playing ... stop")
                media.stop()

            continue

        count_none = 0

        # convert id to string
        id = str(id)
        if id not in tags:
            continue

        if old_id != tags[id]:
            old_id = tags[id]

            print("read_tags - ID:", id)
            print("read_tags - Text:", tags[id])
            
            media.stop()
            if media.add(tags[id]) == 0:
                print("read_tags - media added a new theme")
                media.play_delayed()

    GPIO.cleanup()

if __name__ == "__main__":
    read_tags(tags)